Endpoint regulator and method for regulating a change in wafer thickness in chemical-mechanical planarization of semiconductor wafers

Abstract

The present invention is an endpoint regulator that controls the endpoint in chemical-mechanical planarization of a semiconductor wafer on a polishing pad. The endpoint regulator has a chuck with a mounting surface to which the wafer is attachable, and a spacer connected to the chuck around the periphery of the wafer. The spacer has a polish-stop face that extends axially downwardly with respect to the mounting surface; at least one of the polish-stop face or the wafer mounting surface is selectively spaceable with respect to the other to space the polish-stop face apart from the mounting surface by a distance equal to a desired post-planarization thickness of the wafer. In operation, the polish-stop face engages the polishing pad when the wafer is polished to the desired thickness to substantially prevent further planarization of the wafer. To selectively change the desired endpoint of a wafer, the spacer is either interchanged with a different spacer or adjusted to move the polish-stop face with respect to the mounting surface.

I claim: 
     
       1. An endpoint regulator for controlling the endpoint of a semiconductor wafer in semiconductor chemical-mechanical planarization processes, comprising: a chuck having a mounting surface to which the wafer is attachable; and   a spacer connected to the chuck and substantially surrounding the chuck around the periphery of the wafer, the spacer having a polish-stop face extending axially downwardly with respect to the mounting surface, wherein one of the polish-stop face or the mounting surface is selectively spaceable with respect to the other to space the polish-stop face apart from the mounting surface by a distance equal to a desired post-planarization thickness of the wafer, whereby the polish-stop face is adapted to engage a planarizing surface of a semiconductor polishing pad when the thickness of the wafer is substantially at the desired post-planarization thickness to substantially prevent further planarization of the wafer.   
     
     
       2. The endpoint regulator of claim 1 wherein the spacer comprises a removably attachable ring having an axial length between a reference point and the polish-stop face, the reference point on the ring being alignable with a guide point on the chuck to selectively space the polish-stop face apart from the mounting face by a distance equal to the desired thickness of the wafer. 
     
     
       3. The endpoint regulator of claim 2 wherein the spacer comprises a plurality of interchangeable rings with different axial lengths, each ring being separately removably attachable to the chuck, wherein a selected ring with an appropriate axial length is attached to the chuck to selectively space the polish-stop face on the selected ring apart from mounting surface by a distance equal to the desired wafer thickness. 
     
     
       4. The endpoint regulator of claim 1 wherein the spacer comprises an axially moveable sleeve, the sleeve being moveable axially with respect to the mounting surface to adjust the space between the mounting surface and the polish-stop face. 
     
     
       5. The endpoint regulator of claim 4 wherein the chuck has threads on an exterior surface and the sleeve has mating threads on an interior surface, the sleeve being axially moveable with respect to the chuck by rotating the sleeve around the chuck. 
     
     
       6. The endpoint regulator of claim 4 wherein an actuator has a housing attached to the chuck and a rod attached to the sleeve, the actuator telescopically moving the sleeve along the chuck to position the polish-stop face with respect to the mounting surface. 
     
     
       7. The endpoint regulator of claim 5, further comprising locking means to prevent the sleeve from rotating with respect to the chuck. 
     
     
       8. The endpoint regulator of claim 7 wherein the locking means comprises a locking ring threadedly attached to the chuck. 
     
     
       9. The endpoint regulator of claim 1 wherein the chuck comprises a wafer carrier and a separate wafer holder, the wafer holder being removably attachable to the wafer carrier, wherein the wafer mounting surface is formed on one side of the wafer holder and the spacer extends axially away from the wafer mounting surface. 
     
     
       10. The endpoint regulator of claim 1 wherein the wafer mounting surface is a lower face of a separate removably attachable backplate. 
     
     
       11. An endpoint regulator for controlling the endpoint of a semiconductor wafer in semiconductor chemical-mechanical planarization processes, comprising: a chuck having a mounting surface to which the wafer is attachable;   a spacer connected to the chuck around the periphery of the wafer, the spacer having a polish-stop face extending axially downwardly with respect to the mounting surface, wherein one of the polish-stop face or the mounting surface is selectively spaceable with respect to the other to space the polish-stop face apart from the mounting surface by a distance equal to a desired post-planarization thickness of a wafer, whereby the polish-stop face is adapted to engage a planarizing surface of a semiconductor polishing pad when the thickness of the wafer is substantially at the desired post-planarization thickness to substantially prevent further planarization of the wafer; and   a sensor attached to the spacer for generating a response signal when the polish-stop face engages the polishing pad.   
     
     
       12. The endpoint regulator of claim 11 wherein the sensor is a light emitter and a light detector, the light emitter directing a beam of light through a channel to the light detector, wherein the beam of light is interrupted when the polish-stop face engages the pad. 
     
     
       13. In chemical-mechanical planarization of semiconductor wafers, a method for regulating the endpoint of a wafer, comprising: providing a spacer with an appropriate axial length between a reference point and a polish-stop face, the spacer surrounding substantially surround a chuck around the periphery of the wafer;   aligning the reference point on the spacer with a guide point on the chuck;   connecting the spacer to the chuck, the polish-stop face being positioned away from a mounting surface on the chuck by a distance equal to a desired post-planarization thickness of the wafer;   attaching the wafer to the chuck;   pressing the wafer against a polishing pad in the presence of a slurry; and   moving at least one of the wafer and the polishing pad with respect to the other until the polish-stop face engages the polishing pad.   
     
     
       14. The method of claim 13, further comprising sensing when the polish-stop face engages the polishing pad. 
     
     
       15. In chemical-mechanical planarization of semiconductor wafers, a method for regulating the endpoint of a wafer, comprising the steps of: providing a chuck having a spacer connected to the chuck and substantially surrounding the chuck around the periphery of the wafer;   moving the spacer axially with respect to the chuck to position a polish-stop face of the spacer apart from a wafer mounting surface of the chuck by a distance equal to a desired post-planarization thickness of the wafer;   attaching the wafer to the chuck;   pressing the wafer against a polishing pad in the presence of a slurry; and   moving at least one of the wafer and the polishing pad with respect to the other until the polish-stop engages the polishing pad.   
     
     
       16. The method of claim 15 wherein the spacer and chuck are threadedly engaged with each other, the moving step comprising rotating the spacer with respect to the chuck to move the polish-stop face a predetermined distance. 
     
     
       17. The method of claim 15 wherein an axial actuator is attached to the chuck and the spacer, the moving step comprising axially moving a rod of the actuator against the spacer to move the polish-stop face a predetermined distance. 
     
     
       18. In chemical-mechanical planarization of semiconductor wafers, a method for regulating the endpoint of a wafer, comprising the steps of: moving a spacer axially with respect to a chuck to position a polish-stop face of the spacer apart from a wafer mounting surface of the chuck by a distance equal to a desired post-planarization thickness of the wafer;   attaching the wafer to the chuck;   pressing the wafer against a polishing pad in the presence of a slurry;   moving at least one of the wafer and the polishing pad with respect to the other until the polish-stop face engages the polishing pad; and   sensing when the polish-stop face engages the polishing pad by providing a sensor attached to the spacer and generating a response signal when the polish-stop face engages the polishing pad.   
     
     
       19. The method of claim 18 wherein the sensing step comprises directing a beam of light from a light emitter to a light detector so that the light beam is interrupted when the polish-stop face engages the pad, and indicating when the light beam is interrupted. 
     
     
       20. A planarizing machine for chemical-mechanical planarization of a semiconductor wafer, comprising: a platen to which a polishing pad is attached;   a wafer chuck positioned opposite the polishing pad, the chuck having a mounting surface to which the wafer is attachable, wherein at least one of the chuck or the platen is movable with respect to the other to engage the wafer with the polishing pad and to impart motion between the wafer and the polishing pad; and   a spacer connected to the chuck and substantially surrounding the chuck around the periphery of the wafer, the spacer having a polish-stop face extending axially downwardly with respect to the mounting surface, wherein one of the polish-stop face or the mounting surface is selectively spaceable with respect to the other space the polish-stop face apart from the mounting surface by a distance equal to a desired post-planarization thickness of the wafer, whereby the polish-stop face is adapted to engage a planarizing surface of the polishing pad when the thickness of the wafer is substantially at the desired post-planarization thickness to substantially prevent further planarization of the wafer.   
     
     
       21. The planarizing machine of claim 20, further comprising a wafer carrier and an actuator attached to the wafer carrier for moving the wafer carrier with respect to the platen, wherein the chuck is a separate unit attachable to the carrier. 
     
     
       22. The planarizing machine of claim 20 wherein the spacer comprises a removably attachable ring having an axial length between a reference point and the polish-stop face, the reference point on the ring being alignable with a guide point on the chuck to selectively space the polish-stop face apart from the mounting face by a distance equal to the desired thickness of the wafer. 
     
     
       23. The planarizing machine of claim 22 wherein the spacer comprises a plurality of interchangeable rings with different axial lengths, each ring being separately removably attachable to the chuck, wherein a selected ring with an appropriate axial length is attached to the chuck to selectively space the polish-stop face on the selected ring apart from mounting surface by a distance equal to the desired wafer thickness. 
     
     
       24. The planarizing machine of claim 20 wherein the spacer comprises an axially moveable sleeve, the sleeve being moveable axially with respect to the mounting surface to adjust the space between the mounting surface and the polish-stop face. 
     
     
       25. The endpoint regulator of claim 24 wherein the chuck has threads on an exterior surface and the sleeve has mating threads on an interior surface, the sleeve being axially moveable with respect to the chuck by rotating the sleeve around the chuck. 
     
     
       26. The planarizing machine of claim 24 wherein an actuator has a housing attached to the chuck and a rod attached to the sleeve, the actuator telescopically moving the sleeve along the chuck to position the polish-stop face with respect to the mounting surface. 
     
     
       27. The planarizing machine of claim 24, further comprising locking means to prevent the sleeve from rotating with respect to the chuck. 
     
     
       28. The planarizing machine of claim 27 wherein the locking means comprises a locking ring threadedly attached to the chuck. 
     
     
       29. The planarizing machine of claim 20 wherein the chuck comprises a wafer carrier and a separate wafer holder, the wafer holder being removably attachable to the wafer carrier, wherein the wafer mounting surface is formed on one side of the wafer holder and the spacer extends axially away from the wafer mounting surface. 
     
     
       30. The planarizing machine of claim 20, further comprising a sensor attached to the spacer for sensing when the polish-stop face engages the polishing pad. 
     
     
       31. The planarizing machine of claim 20 wherein the sensor is a light emitter and a light detector, the light emitter directing a beam of light through a channel to the light detector, wherein the beam of light is interrupted when the polish-stop face engages the pad.